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Pilot Shaft to Bronze Pilot Bushing Clearance

17K views 23 replies 10 participants last post by  1966Mike 
#1 ·
Pilot shaft is slightly worn, and it cleaned up and polished to .587". Dorman pilot bushing measures .593, for total clearance of .006"
Runout in pilot bushing measures less than .001".
Bellhousing runout measures less than .003" in both directions. (ie, north-south and east-west).
Will the somewhat sloppy pilot shaft give me problems?

Thanks in advance,
Joe
 
#4 · (Edited)
Also,in many cases " post install " the ID of the stock type pilot bushings is reduced significantly/enough (due to a very tight interfearance fit) to cause issues with even worn input shafts not being able to fully seat/enter the pilot busing not allowing trans to properly/fully seat against bell hosuing.

I have run into this 1st hand on the last 4 of 4 motor installs on man trans chevelles i have done in past few yrs.

I had to use a dremel tool with fine grinder to carefully/as evenly as possible remove just enough material to allow the input shaft to enter the bushing.

No issues post doing that on those cars 1 of which was my car that has gone over 7kmiles since doing that .

BYW,i have been at this stuff for over 40yr now and havent had any issues with input shafts not going into pilot bushngs post install untill the last 4-5 yrs when the mfg of some pilot buyshings went off shore.

And that includes my cars motor that i have owned for over 33yrs where motor and trans were out a few times over the 33 +yrs with same crank in motor the motor so no change there at all and no damage to crank where pilot bushing seats either.

The mfg tollerance & or metarial the pilot bushing are made of must have changed a bit over the yrs which why we are now having this issue that i see other fellow t/cr's had issues with over past few yrs too.

So do yourself a favor and install the pilot bushing in the crank with motor on hoist/cherry picker
& then prior to installing flywheel,clutch bellhousing have a buddy help you try test fitting input shaft of trans into pilot bushing to see if it still fite post insl;aloing bushing in crank.

I learned this the hard way the 1st time this happened to me a few yrs back.

If it fit's great, but if not it takes litterally 4-5 mins or less to carefully remove enough meterial from the ID of bushing to allow input shaft to properly seat,snug but not too tight all done prior to istalling the flywheel/clutch/bellhousing/and motor in car to find it's an issue.

If you dont test fit you run the risk of getting the motor in car and trans not going in all the way due to thisd issdue having to remove trans/bellhosuing/clutch/flywheel just to take 5 mins to remove enough metrial from bushing to asllow trans to fully/proerly seat.

BTW,i used stock pilot bushings from Doorman/Lakewood/Hayes/Carquest/etc,who knows if they all came from the same mfg or not.

They all looked a little different in color-texture from eachother but all had same non fitment issue post install in every casse weather it be sbc or bbc with muncie trans.

Let us know how it goes.

Scott
 
#5 ·
A piece of emory cloth slipped in a slot hacksawed in end of a short piece of 1/4" dowel rod in a drill will help keep the ID round. Check fit often,a little loose is better than a little tight.Its going to swell with the heat. I have seen the bushing stick to the trans input stub and turn in the crank....makes a rriiiiip noise just as you let out on the clutch,same noise if its way oversize too.
 
#6 ·
A piece of emory cloth slipped in a slot hacksawed in end of a short piece of 1/4" dowel rod in a drill will help keep the ID round. Check fit often,a little loose is better than a little tight.Its going to swell with the heat. I have seen the bushing stick to the trans input stub and turn in the crank....makes a rriiiiip noise just as you let out on the clutch,same noise if its way oversize too.
Speak for yourself, man. :D
 
#8 · (Edited)
Some bushings are slightly magnetic and others are not. Mine is. I have heard that most older ones have less iron content and more bronze. In any case, I put my old worn-out bushing (also a Dorman, magnetic piece) on the stove, and voila! It "sweats" oil which seeps out when it's heated!

I installed the bushing into the crank (the engine is installed in the car) by starting it with a lead hammer. I drove it into place with a cut-off piece of wooden broom handle and a 2 pound ball peen hammer. It took about 20 good whacks to drive it flush with the crank flange, which is where I want it. This position allows full engagement, with about 1/16" clearance between the step in the input shaft and the bushing when the trans is mounted on the bellhousing.

I took your advice and checked the fit of the pilot shaft AFTER the bushing is installed in the crank. I put EXACTLY ONE non-overlapping layer of electrical tape over the pilot end of the plastic alignment tool, miked it and it measures EXACTLY same as my trans pilot shaft. The "test" pilot shaft now barely fits into the new bushing which is now installed into the crank. WOW............that means that after installation, that bushing's ID decreased by .004-.005, because I figure I've now got (about) .001 clearance between the shaft and the bushing. You recall that it was .006" before I installed it on the crank. I verified with an extra Dorman bushing I have, and sure enough, it's sloppy at .006" clearance.

Question: Is there any way that a new bushing can be slightly cocked on installation? Since the bushing is 3/4" deep, you would think that it would straighten itself out if it is "started" slightly cocked, but by the time it is driven in to its full depth that it would end up straight. Thoughts? If this is possible, then would it be necessary to use a press to install the bushing on a uninstalled crank in order to ensure the pilot is installed dead straight? Could the bushing have deformed given the way I installed it?

Joe
 
#10 · (Edited)
Wellllllllllll .....................OK I can see why you would say that.:yes:

I didn't mention that this is the THIRD fookin' bronze bushing that has gotten boogered (hole expanded about 1/8" bigger than the pilot shaft), over the course of the last few years..............less than 7000 miles.:(

Trans is a PITA to R&R...............I'm gettin' too old for this crap.:beers:

Dunno.......maybe this is normal. If so, then what's the point of the Goddam thing. I would think that normal wear would see MAYBE 1/32" expansion at every clutch change, which would be (about) every 40,000 miles. Or, if you're like me and drive the car like it's supposed to be driven (hard), then every 20,000 miles.:D
 
#11 ·
Used a brand new Lakewood(?) bronze and pulled my trans at 40 miles for a repair. Like yours mine had some wear in it and a small lip part way in.
I left it alone and like you have a little slop in the input shaft, not too bad.
How bad could it be with those miles I thought so left it in.
 
#17 ·
Thanks Jody next time around Ill pick one up. Depressing a Lakewood piece may have steel in it? Thought the name would bring some quality.

Anyway the stock bellhousing does not fit quite as tight on the dowels as the scattershield did but it was somewhat snug.

S.C. was a bolt on piece dont know how I would have dial indicated it. Maybe Im ignorant but I imagine to change things would have needed to wallow out the holes for the dowles some?

Trans to S.C fit was super precise. (uses dowel pins also.)

Hope that didnt cause my trans to fail.
 
#19 ·
At least 3/8", with the GM pilot, which is 3/4" deep. If you drive it into the crank so that it is just flush with the surrounding surface, you should have full contact where the step in the pilot shaft is about 1/32" clear of the end of the bushing. It is an easy matter to measure this first.
 
#20 ·
I measured some new pilot bushing bores and they come in at .593". I installed a new pilot bushing into a 400 small block crankshaft and it still measured .593".

I have also measured some new maindrive gear tips today and they all measure in at .590".

There is a clearance of .003" measuring new parts.
 

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#21 ·
I know this thread is quite old, however recently I’ve had issues with a fairly new drivetrain, for some reason my transmission (M20) is not slowing down internally once the clutch is depressed at slow vehicle speeds or at a stop. I’ve had the transmission and bellhousing off 3 times in 2 weeks chasing what I thought was a geometery issue with the clutch linkage causing poor release. After verifying my pivot ball heights, flywheel deck thickness and bellhousing runout (both parallel and concentric to the crank) I changed the pilot bushing, this is where it starts to get weird. Now a standard manual trans pilot bushing that comes with any clutch kit does not fit in the end of my crank (6223 big block truck crankshaft) , I’ve changed this bushing myself twice now and each time I’ve had to put it in the lathe and take it down to 1.060” to create a .0025” interference fit in the crank pilot bushing bore. No big deal, however after the last clutch changeout I notice my pilot bushing was worn 1/16th of an inch larger that my input shaft of my transmission pilot. I might add that this bushing had maybe 500 miles on it , the clutch had slipped hard on a good 2nd - 3rd shift so needed to be replaced. Ok so new bushing, new clutch , no issues until the drivetrain is warm, again. Pull it back apart, bushing has considerable wear for the 75miles that are on it. I remove the bushing and flywheel and decided to put an indicator on the pilot bushing hole. The hole read for a total of .040 non concentric runout, due to the fact that this crankshaft from the factory was designated for a truck which used an entirely different pilot bearing setup so the pilot bushing hole location was never properly machined, the rough hole was there ( wrong size for the bushing of course) but was never machine concentric to the crank and thus causes the drag issue on my transmission when hot , not to mention added stress to my front bearing. The fix? A custom bushing that uses the larger diameter hole meant for a truck pilot bearing, which has a measured runout of .002”. I hope somebody reads this , it might help put some of their issues to bed or keep them from chasing a clutch release issue which isn’t there. Thanks
 
#24 ·
This bushing fits into the larger machined portion designed for a truck pilot bearing, ultimately a sealed ball bearing would be ideal, this works well for now issue solved. The entire pilot tip is supported as the bushing extends into the original smaller hole as a loose fit. The front of the bushing is clearenced for the input shaft but I’m my case since I’m using a block save plate the clearance is not an issue.
 
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